DEVELOPMENTOFTHERESONANT-CAVITYVIRTUAL-CATHODE ANDLARCE-ORBITGYR~TRONHIGH-POWERMICROWAVESOURCES*

At Los Alamos National Laboratory, research is continuing on the development of both the resonant-cavity virtual-cathode source and the large-orbit gyrotron highpower microwave source. The resonant-cavity virtualcathode development effort has succeeded in demonstrating narrow-band, single-mode operation of this typically wideband source. This is accomplished by supplying feedback to the oscillating virtual cathode with a resonant-cavity structure. The large-orbit gyrotron effort is developing a method for efficiently coupling the microwave power from the device so that it can be easily used as a high-power microwave generator for accelerator applications. A repetitive pulse capability is also being developed for both microwave sources. Experimental results are presented in this paper. Background There is a continuing demand for ever more powerful and efficient RF power sources to drive the RF accelerating structures used to accelerate particle beams. The need for very high power, far exceeding the capability of commerically available microwave tubes, becomes quite evident as one reviews the proposed designs for future linear colliders. The RF power requirement for these machines is in the terawatt regime and the required frequency is in the lo- to 30-GHz range. A wide range of alternative high-power microwave sources is being investigated at various laboratories. These include the (1) relativistic klystron, (2) lasertron, (3) magnetically insulated line oscillator (MILO), (4) gyroklystron and gyrotron, (5) virtual-cathode-based sources, and (6) the large-orbit gyrotron. At present, no candidate has emerged as the clear source of choice, and the related technologies are very immature when compared with the klystron technology that has matured over the last 40 years. This paper will describe the progress at Los Alamos on two of these sources: (1) the large-orbit gyrotron (LOG) and (2) the resonant-cavity virtual-cathode source. Large-Orbit Gyrotron